/* Integer base 2 logarithm calculation
 *
 * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#ifndef _LINUX_LOG2_H
#define _LINUX_LOG2_H

#include <linux/fls.h>
#include <linux/fls64.h>
#include <linux/types.h>
#include <linux/bitops.h>

/*
 * non-constant log of base 2 calculators
 * - the arch may override these in asm/bitops.h if they can be implemented
 *   more efficiently than using fls() and fls64()
 * - the arch is not required to handle n==0 if implementing the fallback
 */
#ifndef CONFIG_ARCH_HAS_ILOG2_U32
static inline __attribute__((const)) int __ilog2_u32(u32 n)
{
	return fls(n) - 1;
}
#endif

#ifndef CONFIG_ARCH_HAS_ILOG2_U64
static inline __attribute__((const)) int __ilog2_u64(u64 n)
{
	return fls64(n) - 1;
}
#endif

/*
 *  Determine whether some value is a power of two, where zero is
 * *not* considered a power of two.
 */

static inline __attribute__((const)) bool is_power_of_2(unsigned long n)
{
	return (n != 0 && ((n & (n - 1)) == 0));
}

/*
 * round up to nearest power of two
 */
static inline __attribute__((const)) unsigned long
__roundup_pow_of_two(unsigned long n)
{
	return 1UL << fls_long(n - 1);
}

/*
 * round down to nearest power of two
 */
static inline __attribute__((const)) unsigned long
__rounddown_pow_of_two(unsigned long n)
{
	return 1UL << (fls_long(n) - 1);
}

/**
 * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value
 * @n - parameter
 *
 * constant-capable log of base 2 calculation
 * - this can be used to initialise global variables from constant data, hence
 *   the massive ternary operator construction
 *
 * selects the appropriately-sized optimised version depending on sizeof(n)
 */
#define ilog2(n)                                                               \
	(__builtin_constant_p(n) ?                                             \
		 ((n) < 2 ? 0 :                                                \
			    (n) & (1ULL << 63) ?                               \
			    63 :                                               \
			    (n) & (1ULL << 62) ?                               \
			    62 :                                               \
			    (n) & (1ULL << 61) ?                               \
			    61 :                                               \
			    (n) & (1ULL << 60) ?                               \
			    60 :                                               \
			    (n) & (1ULL << 59) ?                               \
			    59 :                                               \
			    (n) & (1ULL << 58) ?                               \
			    58 :                                               \
			    (n) & (1ULL << 57) ?                               \
			    57 :                                               \
			    (n) & (1ULL << 56) ?                               \
			    56 :                                               \
			    (n) & (1ULL << 55) ?                               \
			    55 :                                               \
			    (n) & (1ULL << 54) ?                               \
			    54 :                                               \
			    (n) & (1ULL << 53) ?                               \
			    53 :                                               \
			    (n) & (1ULL << 52) ?                               \
			    52 :                                               \
			    (n) & (1ULL << 51) ?                               \
			    51 :                                               \
			    (n) & (1ULL << 50) ?                               \
			    50 :                                               \
			    (n) & (1ULL << 49) ?                               \
			    49 :                                               \
			    (n) & (1ULL << 48) ?                               \
			    48 :                                               \
			    (n) & (1ULL << 47) ?                               \
			    47 :                                               \
			    (n) & (1ULL << 46) ?                               \
			    46 :                                               \
			    (n) & (1ULL << 45) ?                               \
			    45 :                                               \
			    (n) & (1ULL << 44) ?                               \
			    44 :                                               \
			    (n) & (1ULL << 43) ?                               \
			    43 :                                               \
			    (n) & (1ULL << 42) ?                               \
			    42 :                                               \
			    (n) & (1ULL << 41) ?                               \
			    41 :                                               \
			    (n) & (1ULL << 40) ?                               \
			    40 :                                               \
			    (n) & (1ULL << 39) ?                               \
			    39 :                                               \
			    (n) & (1ULL << 38) ?                               \
			    38 :                                               \
			    (n) & (1ULL << 37) ?                               \
			    37 :                                               \
			    (n) & (1ULL << 36) ?                               \
			    36 :                                               \
			    (n) & (1ULL << 35) ?                               \
			    35 :                                               \
			    (n) & (1ULL << 34) ?                               \
			    34 :                                               \
			    (n) & (1ULL << 33) ?                               \
			    33 :                                               \
			    (n) & (1ULL << 32) ?                               \
			    32 :                                               \
			    (n) & (1ULL << 31) ?                               \
			    31 :                                               \
			    (n) & (1ULL << 30) ?                               \
			    30 :                                               \
			    (n) & (1ULL << 29) ?                               \
			    29 :                                               \
			    (n) & (1ULL << 28) ?                               \
			    28 :                                               \
			    (n) & (1ULL << 27) ?                               \
			    27 :                                               \
			    (n) & (1ULL << 26) ?                               \
			    26 :                                               \
			    (n) & (1ULL << 25) ?                               \
			    25 :                                               \
			    (n) & (1ULL << 24) ?                               \
			    24 :                                               \
			    (n) & (1ULL << 23) ?                               \
			    23 :                                               \
			    (n) & (1ULL << 22) ?                               \
			    22 :                                               \
			    (n) & (1ULL << 21) ?                               \
			    21 :                                               \
			    (n) & (1ULL << 20) ?                               \
			    20 :                                               \
			    (n) & (1ULL << 19) ?                               \
			    19 :                                               \
			    (n) & (1ULL << 18) ?                               \
			    18 :                                               \
			    (n) & (1ULL << 17) ?                               \
			    17 :                                               \
			    (n) & (1ULL << 16) ?                               \
			    16 :                                               \
			    (n) & (1ULL << 15) ?                               \
			    15 :                                               \
			    (n) & (1ULL << 14) ?                               \
			    14 :                                               \
			    (n) & (1ULL << 13) ?                               \
			    13 :                                               \
			    (n) & (1ULL << 12) ?                               \
			    12 :                                               \
			    (n) & (1ULL << 11) ?                               \
			    11 :                                               \
			    (n) & (1ULL << 10) ?                               \
			    10 :                                               \
			    (n) & (1ULL << 9) ?                                \
			    9 :                                                \
			    (n) & (1ULL << 8) ?                                \
			    8 :                                                \
			    (n) & (1ULL << 7) ?                                \
			    7 :                                                \
			    (n) & (1ULL << 6) ?                                \
			    6 :                                                \
			    (n) & (1ULL << 5) ?                                \
			    5 :                                                \
			    (n) & (1ULL << 4) ?                                \
			    4 :                                                \
			    (n) & (1ULL << 3) ? 3 :                            \
						(n) & (1ULL << 2) ? 2 : 1) :   \
		 (sizeof(n) <= 4) ? __ilog2_u32(n) : __ilog2_u64(n))

/**
 * roundup_pow_of_two - round the given value up to nearest power of two
 * @n - parameter
 *
 * round the given value up to the nearest power of two
 * - the result is undefined when n == 0
 * - this can be used to initialise global variables from constant data
 */
#define roundup_pow_of_two(n)                                                  \
	(__builtin_constant_p(n) ?                                             \
		 ((n == 1) ? 1 : (1UL << (ilog2((n)-1) + 1))) :                \
		 __roundup_pow_of_two(n))

/**
 * rounddown_pow_of_two - round the given value down to nearest power of two
 * @n - parameter
 *
 * round the given value down to the nearest power of two
 * - the result is undefined when n == 0
 * - this can be used to initialise global variables from constant data
 */
#define rounddown_pow_of_two(n)                                                \
	(__builtin_constant_p(n) ? ((1UL << ilog2(n))) :                       \
				   __rounddown_pow_of_two(n))

/**
 * order_base_2 - calculate the (rounded up) base 2 order of the argument
 * @n: parameter
 *
 * The first few values calculated by this routine:
 *  ob2(0) = 0
 *  ob2(1) = 0
 *  ob2(2) = 1
 *  ob2(3) = 2
 *  ob2(4) = 2
 *  ob2(5) = 3
 *  ... and so on.
 */

static inline __attribute_const__ int __order_base_2(unsigned long n)
{
	return n > 1 ? ilog2(n - 1) + 1 : 0;
}

#define order_base_2(n)                                                        \
	(__builtin_constant_p(n) ?                                             \
		 (((n) == 0 || (n) == 1) ? 0 : ilog2((n)-1) + 1) :             \
		 __order_base_2(n))
#endif /* _LINUX_LOG2_H */
